private byte[] GetLargeItemSegment(PageHeaderBase header, IPage page, long startIndex, long endIndex)
{
if (PageFormatter.ReadMultipageItemLength(page) <= endIndex)
{
throw new ArgumentOutOfRangeException(nameof(endIndex));
}
var length = endIndex - startIndex + 1;
var result = new byte[length];
long sourceOffset = 0;
long destOffset = 0;
// navigate through large item
while (true)
{
var readBytes = PageFormatter.ReadMultipageItemBlock(page, Math.Min(_pageManager.PageSize, (int)(endIndex + 1 - sourceOffset)));
sourceOffset += readBytes.Length;
if (sourceOffset > startIndex)
{
var ssi = sourceOffset - startIndex - 1 < readBytes.Length
? startIndex + readBytes.Length - sourceOffset
: 0;
var l = readBytes.Length - Math.Max(0, sourceOffset - endIndex - 1) - ssi;
Array.Copy(readBytes, ssi, result, destOffset, l);
destOffset += l;
if (sourceOffset >= endIndex)
{
return(result);
}
}
var nextPageIndex = ((MultipageItemPageHeader)header).NextPageIndex;
if (nextPageIndex != -1)
{
page = _pageManager.FetchPage(nextPageIndex);
header = PageFormatter.GetPageHeader(page);
}
}
}
/// <summary>
/// Gets DbItem instance by reference.
/// </summary>
/// <param name="reference">Reference to the requested db item</param>
/// <returns></returns>
public DbItem Get(DbItemReference reference)
{
if (!_pageManager.PageExists(reference.PageIndex))
{
return(null);
}
IPage page = _pageManager.FetchPage(reference.PageIndex);
var header = PageFormatter.GetPageHeader(page);
if (header.SizeRange == SizeRange.MultiPage)
{
var length = PageFormatter.ReadMultipageItemLength(page);
var content = new byte[length];
long offset = 0;
while (page != null)
{
var readBytes = PageFormatter.ReadMultipageItemBlock(page, Math.Min(_pageManager.PageSize, (int)(length - offset)));
readBytes.CopyTo(content, offset);
offset += readBytes.Length;
var nextPageIndex = ((MultipageItemPageHeader)header).NextPageIndex;
if (nextPageIndex != -1)
{
page = _pageManager.FetchPage(nextPageIndex);
header = PageFormatter.GetPageHeader(page);
}
else
{
page = null;
}
}
return(new DbItem(content));
}
return(PageFormatter.IsFixedSizeItemAllocated(page, reference.ItemIndex)
? PageFormatter.ReadFixedSizeItem(page, reference.ItemIndex)
: null);
}
